The term “organic substrate” denotes herein waste, by-products and coproducts formed from organic matter, i.e. from biomass. The term “substrate” will subsequently be preferentially used.
The exploitation of such organic substrates resulting from human activities, whether they are domestic, industrial, agricultural or agro-industrial, can be implemented by means of fermentation processes. Depending on the purpose of the fermentation, the production of various metabolites is promoted, for example methane, hydrogen, volatile fatty acids, alcohols or the like. Processes for treating organic waste for the purpose of producing various metabolites are known, for example those described by EP-A-796 832, WO-A-2009/093 926 and WO-A-2011/120 035 in which a prior heat treatment of the organic matter is carried out, aimed at pasteurizing or sterilizing the organic matter in order to control the fermentation parameters.
The fermentable potential is a parameter used as an indicator of the effectiveness of a fermentation of a given biomass for producing metabolites, whatever the fermentative route implemented.
It proves to be the case that the fermentable potential rapidly evolves over time for fresh substrate which has not undergone any treatment. In other words, in the absence of treatment, the capacity of an organic substrate to produce metabolites decreases rapidly over time. This implies that the fresh substrate, which is generally relatively moist, whatever its nature, should be used rapidly. Typically, the use occurs within seven to fifteen days following collection, whether the fermentation is carried out in solid phase or in liquid phase, in order to preserve an optimal yield of metabolite production by fermentation.
As it happens, in the context of an industrial fermentation process, it is important, in order to guarantee the productivity of the facility, to have a substrate of which the fermentable potential is not only as high as possible, but especially regular and controlled. This point is all the more important since the substrates used in an industrial fermentation process are mainly of agricultural, industrial. domestic and/or food-processing origin in order to guarantee large volumes. As a result, qualitative and quantitative variability in the substrate, for example according to the season, is observed. By way of illustration, when farm animals, such as cattle, sheep or goats, are grazing outside, typically during the summer months, the production of dung and liquid manure is minimal. Likewise, green waste (clippings, leaves, etc.) are virtually nonexistent in winter. In other words, it is difficult to obtain a continuous and regular volume of a substrate of which the composition and the fermentable potential are controlled throughout the year. Indeed, it is generally accepted that storage of the substrate does not make it possible to maintain the fermentable potential of the substrate at desired values. In other words, it is accepted that rapid use of the substrate is necessary in order to preserve an optimal fermentable potential.